Police and armoured vehicles flooded Minsk central square in Belarus this evening in preparation for a standoff with the opposition, who plan to turn out in force to challenge early election results that give Alexander Lukashenko victory in the country's presidential vote.

Exit polls give Lukashenko, 72% of the vote; his closest competitor, the former deputy foreign minister, Andrei Sannikov, has just 6.33%. Nine candidates are challenging Lukashenko in the vote.

The opposition failed to unite around a single candidate to challenge Lukashenko, who has ruled the country since 1994 and has been dubbed "Europe's last dictator". They plan to join forces for a protest set for when polling stations shut that is expected to gather tens of thousands of people. "It's getting more and more tense," Yaroslav Romanchuk, a presidential candidate, said by telephone from Minsk. "We don't know what kind of a situation it will be as downtown is full of police."

Internet sites, including major email carriers such as Gmail and Yahoo, have been blocked. Opposition candidates complained that dozens of their supporters had been held since the eve of the vote.

Citing exit polls released by Inside, an independent polling agency, Romanchuk said Lukashenko had failed to garner the 50% needed to win the election without a second round. According to the survey, Lukashenko was polling at 38% this afternoon, while the nine opposition candidates combined stood at 43.5%.

Lukashenko has vowed to deal harshly with the opposition. "I don't conduct any dialogue with bandits and saboteurs," he was quoted by news agencies in Minsk.

For much of the year, Lukashenko appeared to be easing his grip on the former Soviet nation, as he flirted with the west amid deteriorating relations with his traditional sponsor, Russia. A visit to Moscow this month, boosted by the signing of preferential trade deals, sealed his tilt towards the Kremlin.

The EU has offered Belarus a ?3bn (?2.5bn) aid package if the elections are declared free and fair. Observers from the Organisation for Security and Cooperation in Europe are monitoring the elections for the first time.

More than 23% of the country's seven million registered voters voted early, with the opposition accusing the government of widespread ballot stuffing.